Heat-treating furnace



Dec- 27, 1949 w.-.c. HAssELHoRN HEAT TREATING I-iURmacEA FiledvJuly 16. 194.5

Patented Dec. 27, 1949 UNITED STATES PATE. NT overl-.CE

HEAT-TREATING FU-RNACE '/Waller C'. Hasselh'crn, Chicago, Ill., Aassigner to Cook. vElectric Company,. Chicago, Ill., a `-c'orlo- '.rationof Illinois Application'J'uly 16, 1945, ySeria' No. 605.373

15 Claims.

4'I-h-is application relateslto' heat treating 1 apparatus 'and temperature "control means therefor.

more particularly toheat 'treating'apparatus hav- 'inga preheating stage,fa hea-t-holdi'nglstage and a -cooling stage, and-means-m varying the 'rate -of heating-in the-preheating stage and thefrate of cooling inthe coolingcstageyanditis an object rvof the invention 11o-'provide improved'fheat treatas some 'forms of ceramicsyit -is-"n'ecessaryl to have a cycle of temperature variationssuc'h for example kas a cycle including a preheatin'g phase, a 'heat-holding phase, and "a cooling phase.

Moreover, it isdesira'ble that there bena correlation between the various'phases of the heat treating cycle. That istofsay'itmay be desirable to have a rapid ratewof preheating with "a rapid rate of cooling, ora slow rateof' preheating'with a slow rate'of cooling. i-ldditionally',A it ismdesi'rable. that 'the rate of preheating andV the ratev 'of cooling be variablewithin the same. furnace so that there may be rapid preheatingv "as 'well as' 'slow prehe'atingalong With- 'correlated coolingv :phases without providing-Japlurality (1f-furnaces.

Apparatus for heat treatingarti'cles, whereby thev describedf-heat `treat-ing'cycle is obtained, `may cf course .include three ror more separate furnaces `in each 'of which va certain portion'oi' the 'heat treating cycleis carriedon-l Thus'there-may be a preheating'ffurnace; aheatfholding'furnace,

and acooling furnace. lnleachi'of thesefseparate furnaces heating .means-as Well 'as heat 'or 'temperature controlling.' meanswmustbeprovided in Aorder to. give. thedesired properti'e'suin the fm- Thisrresultssinran undue use of ished articles; valuable 'space 'to- -accommodatefthe threeiurhaces. It further-'requiresafconsiderable. amount ofcontrol; equipment., particularly where lit is rnecessary to provide. :a .between the -preheating .rate-v .and the vceoiirrg` rate.. It lalso 55- holdi-ng itin desired'position.

ris necessary, inanarrangement of this character,

to remove the articlesffrom one 4furnace, trans- `lport them to a second-furnace, `andthenremove them `fromthe second lfurnace andtransfer them tothe 'thirdfurriace Heat is; 10st fr'omithe articles 'during transit, lW-iththe' consequent'possibility If p'oorpropeitesinthedinar product.

:Accordingly'fitis a tfurther"'(zibjectol the in-vention to provide an improved heat treating `furnace iin Vwhich the complete `cycle of operation, preheating, heat-holding,'and cooling, is carried on within 'the samefurnace. v

In carrying'out.the'linventionin oneiorrm-heat treating apparatus .is .provided comprising an elongated `chamber :having '-a. normal position. ".-l-Eeatin'g meansffare associated-'with thelchamber .centrally"thereofV for maintaining "a temperature distribution therein, and inord'e'rfto vary the temperature distribution throughout the elongated 20-l '.displaced 'from its normal position. More parchamber the chamberis pivoted' sothat itr maybe t-cularly, the he'atv-treatingrturnacevincludes "an elongated chamber having aprehe'ating portion, a heat-holding portion', and `a cooling portion.

. Heating means are associated with vthe vchamber intheheat-holding portion thereof for maintain- .ing the temperature 'distribution' therein. The

elongatedY cham-boris pivotall-y mounted. whereby it [may bedisplaced-f-rom'V anormal :posi-tion, and

inlet-and-outletfmeans are provided'adj acent each endof, the .chamber whereby Yconvection currents of `air l may pass theretlfn'ough when thechamber `is displaced from; itsnormal position'.

For a more complete understanding olf the invention, reference Vvshould. now be had to the accompanying. drawing in which.;

Figure 1. isv a A,perspective view of a furnace embodying the invention;` v

Fig. 2 is a somewhat. enlarged sectional view takenV substantiallyialong the line 2 2. of Fig. 1;

Fi'g...3 is a similar sectional View of a modified vform 'of the invention;

Fig. 4 is a diagrammaticrepresentation of heattreating cycl'esobtainable with the furnace shown inV Figs. 1 and 3i;

Fig. 5` is anyenlargedlrag'mentary view 'of a 'portion of Fi'g. 1, and

'frames f2 and I3 'at the ends ofthe 'chamber for The elongated chamber I is divided into three different portions or treating chambers i4, i and IES, consecutively arranged so that an article in passing through the furnace moves from the chamber I4, through the chamber I5, and thereafter through the chamber I6. The chambers I4, I5 and Iii may be constructed in any well known manner and may, for example, include a layer Il of refractory material such as fire clay, for example, which will withstand temperatures over 2300 degrees Fahrenheit and a supporting metallic shell I9. The thickness of the layer of refractory material il is sufficient so that substantially none of the heat is transferred to the atmosphere through the furnace walls. The cross section of the chambers I6, i5 and I6 may be of any size to be able to accommodate articles to be treated, and arranged within these chambers is a anged ceramic runway or track 2l upon which trays 23 transporting the articles to be treated move through the furnace. The runway 23 may be made of rebrick having a highly smooth surface so that the trays 23 may be easily pushed therealong. In the operation of the furnace an attendant may push loaded trays through the furnace by using a metal push rod. The length of the chambers I4, I5 and I6 may vary and is dependent upon the range of temperature variation desired.

In one form of the invention, heat may be supplied to the central portion I5 of the furnace by means of the carbon resistance rods 2Q embedded within the refractory material II. The carbon rods extend outwardly from each side of the chamber I5 and are connected by conductors 29 to transformers 25 for supplying electrical current to the resistors. The transformers are of a conventional character and may, for example, be tap-changing transformers, whereby the voltage supplied to the carbon rods is variable to adjust the maximum temperature within the chamber Vl5 asis well understood. Since the refractory material I'I is also electrically insulating, the carbon rods are embedded therein without the provision of any further electrical insulation. The metallic layer I9 has suitable openings provided therein through which the carbon rods 24 extend, and, to insulate the ends of the carbon rods from the surroundings, covers 22 are attached in any suitable way to shell I 9. Openings as shown are provided in the covers 22 through which the insulated conductors 29 pass from the transformers 25 before being attached to the carbon rods, The chambers i4 and l5 may not be provided with heat-supplying or generating means so that they will derive their heat through heat transfer from the chamber I5. The refractory layer VI in the chamber I5 of course is heated to a high temperature by the carbon rods 2li, and through the processes of heat radiation and convection, as well as by conduction, the chambers i4 and I5 will be maintained at a certain temperature and with a certain temperature distribution. The invention is not to be limited to heat generation solely within chamber i5 because it is obvious that the novelty of the structure herein disclosed is also applicable in certain instance to providing some heat generation in either or both of chambers I 4 and i5 as well as in chamber I5.

A pyrometer 26 is mounted on the exterior of the chamber I5 to give an indication of the temperature therein so that an attendant in charge of the furnace may, by varying the taps on the transformers, keep the temperature in the furnace within desired limits.

Adjacent the outer ends of the chambers I4 andY i6, respectively, are the Vents 3I and 32, whereby air or other gases may circulate through the furnace chamber. The vents 3i and 32 include dempers 33 and 34, respectively, by means of which the amount of air or gas circulating through the furnace may be controlled or it may be shut off altogether. In order that the furnace chamber may be completely closed during the time that the heat-treating cycle is being carried out, the door 35 is hinged or otherwise attached to the preheating chamber Id to close this chamber, and the door 36 is similarly attached to the cooling chamber I6 to close this chamber.

In the normal operation of the furnace the doors 35 and 36 are closed and power is supplied to the carbon rods 24 through transformers 25,as described. While carbon rods have been shown only in the bottom of the chamber I5, it will be apparent to those skilled in this art that similar rods may be arranged at the top of the chamber I5 as well as along the sides thereof if this is necessary to produce a temperature or a capacity that is desired. The carbon rods 2li being associated with the chamber I5, this chamber will reach some maximum temperature, for example 2300 degrees Fahrenheit, which is substantially constant throughout the chamber, (adjacent the junctions with chambers I 4 and EG the temperature in chamber I5 is less than the maximum due to the fact that chambers iff:- and I are below the temperature of chamber I5 and thus heat is being transferred to chambers itl and IIS) and through the processes of radiation, conduction and convection, each of the chambers I4 and I5 acquires a certain temperature gradient.

, temperature within the chambers I4 and I6 varies from the temperature of the chamber I5 where the chambers are contiguous to a temperature very much lower, approaching that of the surrounding atmosphere, adjacent the doors 35 and Thus an article moving through the furnace l@ experiences three temperature phases. a rising temperature from approximately ambient to 2300 degrees Fahrenheit in the chamber I4, a constant temperature of 2300 degrees Fahrenheit in the chamber I5, and a decreasing temperature from 2300 degrees Fahrenheit to approximately ambient in the chamber I 6.

In one type of heat-treating cycle the furnace chamber l0 is arranged to be used in the horizontal position as shown; and to produce variation of the temperature gradients inside of the chambers I4, I5 and I6 for other types of heattreating cycles, the chamber I 0 is pivoted or tilted from its normal horizontal position to an angular position such as the one shown by the dotted outline for example. This is accomplished by providing the pivoting framework II beneath the furnace chamber including the two spaced apart frames 3l and 33, each having a center support 39 and two end supports 40 and 4I. The center supports 39 are attached beneath the heatholding chamber I5, the end members 40 are attached beneath the outer end of the preheating chamber I4, and the end members 4I are attached beneath the outer end of the cooling chamber I6.

out of the vent 32.

bers I4 and I6. This is a convection phenomenon.

Gases or other fluids when heated tend to rise because of their decrease in specific gravity. Air in the chamber Ill is heated and tends to rise, and when the chamber I is tilted the air therein is given a pathway to flow in and flows from the lower end toward the higher end. The air en- .tering the vent 3| is at ambient temperature or thereabouts and thus is considerably lower in temperature than exists inside of the chamber I4.

Consequently, the temperature in the chamber 4 is reduced at its beginning and throughout its length by the incoming cold air. The air, in continuing its circulation, becomes heated to a higher temperature in the chamber I5, carries the heat it has acquired into the chamber I6, and consequently raises the temperature therein adjacent the point where the chamber I6 joins the chamber I over the temperature for this point for the horizontal operation, the heated air passing Since the circulating air is at a higher temperature than the temperature in chamber I6, the air is cooled in passing therethrough but it keeps the temperature in chamber I6 including that at the exit end at a value higher than for the normal horizontal operation. This becomes clear by recalling that the heat in chambers I4 and I6 is derived from the heat in chamber I5 by radiation, conduction and convection, and when the furnace is tilted convection comes actively into play.

The area of maximum temperature which, in the horizontal case of furnace operation, exists throughout a substantial portion of chamber i5 has been shifted farther away from the junction of chambers I4 and I5 and into the beginning portions of chamber I6. Thus the distance from the outer end of the chamber I4, where the cold air is coming in, to the area of maximum ten.- perature has been lengthened somewhat. This plus the low entrance temperature-in chamber I4 and the fact that the cool air is only gradually heated results in a low temperature gradient in chamber I4 or the rate of rise of temperature has been decreased over the horizontal case. Also the distance from the area of maximum temperature in the chambers I5 and I6 adjacent the junction of these chambers to the outer end of chamber I6 where the heated air goes out of the vent 3?. has been shortened. However due to this heated air the exit temperature from chamber l5 is much higher than that for horizontal operation.

As a result the articles in chamber I5 are sub- 'jected to a temperature varying from a high value to a value still high and hence are cooled at a low rate (i. e. low temperature gradient) Aeven though the temperature variation takes place in a somewhat shorter distance than for normal operation. Consequently, articles on the tray 23 iwhich are being pushed at uniform intervals through the furnace chambers are heated slowly 'Y in thechamber I4, have their temperature held 1 at the desired level through a portion of the chamber I5 and the beginning portion of the chamber IB, followed by a slow cooling as the articles approach the door 36. The heated air prevents the articles from cooling until they are substantially at the junction of chambers I5 and I5 and then the cooling takes place somewhat more slowly until somewhat farther away from the junction as shown by curve t3. The dotted portion of the curve beyond chamber I6 indicates the cooling in the atmosphere which ordinarily does not effect the properties of the articles. If this should be too rapid the articles may of course be transferred to another furnace for slower coollng.

Assuming in a third instance that it is desired to have a heat-treating cycle having a high rate of preheating, i. e., a rapid rise of temperature in chamber I4, and a rapid rate of cooling, i. e., a rapid decrease in temperature in chamber I, the furnace I0 is tilted in the opposite direction so that the preheating chamber I4 is at a higher level than the cooling chamber I6, which is accomplished by tilting the chamber I0 clockwise and placing the thumbscrews 52 and 59 in theopenings 48 and 58 (shown dotted). This cycle 4is exemplified by the curve t3 in Fig. 4. In this position of the furnace, air circulates in through the vent 32 and out of the vent 3|, due to its change in density and the fact that tilting the furnace provides a pathway for the air to now in, reversing the direction of air flow given in the preceding example. The cold air flowing in the vent 32 cools the chamber I6 since the air is at ambient temperature, and therefore, is much below the temperature in chamber I6, and the cold air, continuing its flow, becomes heated in the chambers I6 and I 5, passing therethrough and through the chamber I4. The cold air .as it enters the chamber I5 cools this chamber, below its maximum temperature adjacent where the chambers I6 and I'5 meet and thus the distance in which the temperature rises from a low value at the vent 32 to its maximum value in the chamber I5 has been increased somewhat. However, since the air entering vent 32 reduces the exit temperature of chamber I6 to a value much below that for horizontal operation and the temperature in chamber I5 remains substantially the same as for horizontal operation, the temperature gradient (rate of cooling) has beeni increased. The heated air moving into chamber I4 of course raises the temperature therein throughout its length over that for horizontal operation, particularly where this chamber joins the chamber I5, and therefore, the area of maximum temperature which existed previously in the chamber I5 is shifted to also include the beginning portion of the chamber I4. The entrance to chamber I4 is therefore at a higher temperature and thus articles to be treated are subjected to a higher initial temperature. The distance in chamber I4 in which the temperature changes from the initial or entrance value to the maximum value is decreased. This plus the higher initial temperature effects an increased temperature gradient in chamber I4 over that existing therein during the normal horizontal operation of the furnace.

through the furnace on the tray y23, these articles are subjected to a temperature which increases rapidly, and consequently, are preheated quickly.

Hence, when articles are moved In this instance of operation also the articles are pushed through the furnace on the trays 23 in steps at uniform intervals so that the articles are subjected to the temperature at regular intervals in the furnace. After `the articles have been rapidly preheated in chamber I4, they are moved through the chamber l and are "exposed to thedesired maximum temperature for 'the necessary Ilength o'f time. When the articles are moved into the chamber |76, they Lare subjected to the temperature inthis -chamber and are cooled over the somewhat greater v"distance from the area -of :maximum Atemperature to the exit of chamber l5. VBut the -heatedarticles trom chamber l5 are subjected to the cool air ilowing in chamber -I and are cooled to an exit tempera'- ture considerably below that existing for -horie zo'rital operation. Consequently lthe articles are cooled from a high value yto a much lower value and -hence are cooled at a rapid rate. The cold aircorftactingthe articles near the end of chamber l5 begins to cool them slightly as shown by the cur-ve and when vthe articles pass into cham-f ber l "away from the heating units of chamber F5 the cooling becomes-more rapid. Thus the articl'esin this examplefc'f 'operation pass through a ycycle beginning with rapid preheating phase, having a heat-holding phase, and ending with a rapid cooling phase (curve Vta, Fig. 4). The dotted portion `of the curve indicates the cooling taking place in vthe atmosphere after the ff articles are removed from the furnace.

I-f it is -foundth'at whenf'the furnace chamber IB vis tilted from the horizontal position and air is entering 'through either vent there may be a tendency for the temperature throughout the whole furnace to change because of the heat acquired by the cold air, an vattendant may change the taps on the power supply transformers to supply sufficient voltage to the resistors 24 to supply sufcient heat to compensate for the change introduced -bythe -flowin'g air.

The structure of the furnace vand' the manner o'f operation as thus far ldescribed have application when `the furnace is operated manually and the regulating mechanism -60' is disconnected. The'regulating mechanism -60 makes the furnace capable of automatic operation and comprises an expansible and contractible member 6I filled with a heat-responsive liquid, and a connecting o'i` push rod 62. Attached rigidly 'toand extending downwardly from the -lower side of the furnace chamber lll is-a projecting stub 63 having a circular slot ltformedV therein at the lower end thereof and a -hole 65 connecting the lslot with the end of the stub, theslot- '64 continuing to the outside of the lpostlt as shown. The expansible and contractible member '6| may consist of a series of bellows-flanges, and projecting upwardly from the upper end thereof is an internally threaded' rpost Y66. y

Extending between the stub 63 andthe post 66 is 'the connecting -or -push rod 6.2. The lpush rod 62 has a central portion lil which may be gripped by an individual -to 'produce a desired setting and at the lower end of which there is'v In order to assemble the push rod 62 to the" regulating mechanism, the thumbscrews 52 and 59 are removed and the furnace chamber is tilted a sufficient distance 'so that the flange S9 may be placed within the slot -6`4 and the threaded portion 68 threaded'into the post 661' sired that fthefurnace be operated on curve trof Ifit is dee' Fig. 5, the push rod E2 is turned so that the portion 68 is threaded into the post $6 a distance sufficient to hold the chamber iLi higher than the chamber i6 by the desired amount. If it is intended to operate the furnace in the horizontal position (curve t2 of Fig. 5),-the push rod t2 is rotated until the chamber ifi is at the same level with vthe-chamber iii, and i?? 'the furnace is to be operated along vthe curve t3 of Fig. 5 the push rod t2 'is rotated still further until the chamber ifi is below the level ofthe chamber |-6 by the necessary amount. With the 'thumbscrews 52 and 5e removed, the only force maintaining the furnace in the necessary position is that exerted by the bellows El and the push ro'd 62.

Extending from the lower end Aof the bellows 6l is a tube l2 connected with a temperature bulb (not shown) insideo'f the chamber i6, for example, -the temperature bulb being influenced by' the temperature therein. The tube 'E2 is `also iiiledwith the temperature responsive flu-id which transmits the temperature vfrom the temperature bulb to the fluid inside of the bellows 6i. As the fluid increases or decreasesin temperature, the bellows expand Vand contract, thereby keeping 'the furnace in a predetermined position. Thus, if the furnace is to operate in the horizontal position with'a certain temperature in chamber it and the temperature in this chamber increases, the bellows -Gi will expand to raise the chamber ill and lower the Vchamber iii, thereby permitting air to enter vent 32 and cool the furnace. Similarly, if the temperature in chamber -l' decreases the bellows contract'and the chamber IE is raised permittingV circulation of air in a vent 3l which increases the temperature in chamber as already explained. ln the event it yis desired to regulate the lposition of the furnace according to the temperature inside of the chamber l5, the tube l2 may be connected to the tube 73 which is in turn connected to 'a temperature bulb y(not shown) inside of the chamber i5.

Referring to Fig. `V3, there vis shown a modication'of the furnace suitable for use with hydro'- gen controlled atmosphere or the like. When a controlled atmosphere is being used, it is- 'necessary to seal al1 openings Ato theV furnace to prevent air from leaking thereinto. To accomplish this the doors 35 and 36 tightly close, and suitable connections Vare provided to the vents 3l and 32 Ato supply the controlled atmosphere. Air is prevented from seeping into the furnace chamber vand the controlled atmosphere is prevented from seeping out of the furnace chamber where the carbon rods 24 vpass through the metal cover! 9 by circular bellows T4 being'placed around the exposed ends of the carbon rods 24 and welded or otherwise sealed to the metal cover i9. Theouter 'end of the bellows l!! is closed by means `of metallic plates 'I5 hai/'ing sealedV connections -28 for conductors 29 to thereby completely seal the furnace.

YWhen the furnaceris being used with a controiled atmosphere, the operation is substantially the same as when air is used. The gas constituting'the'atmosphere enters the'furnace through either of the vents '3i or 32, or otherwise, and since the temperature of this gas is ordinarilyat about ambient temperature the vdifferent temperature gradients within the furnace may be obtained by tiltingl the furnace chamber substantially, as already described. If it is intendi ed that the furnace operate in the horizontal po-v l l sition and it is necessary to have the gas of the atmosphere circulate therethrough, the gas may be pumped through the vents 3l or 32 in any well known manner such as by a centrifugal pump (not shown).

Along with tilting the furnace chamber from the hoizontal and allowing gases whether air or otherwise to circulate through the vents 3l and 32 to effect a change in the temperature gradients existing within the furnace, it may be desirable to have the type of temperature gradient associated with a particular direction of tilt of the furnace, but with a somewhat different temperature variation. This temperature variation may be obtained by opening or closing the dampers 33 and 34 to vary the amount of gas flowing through the furnace chamber. Thus, if the dampers are completely open the maximum amount of air circulates, and consequently, the

cooler is the end of the furnace chamber at which the air enters and closing the dampers decreases the amount of gas circulating, and hence, results in a lesser temperature change.

increasing or decreasing the amount of air circulating will of course also vary the temperi ature within the chamber l5, and in this manner small temperature changes in the chamber I5 may be obtained without varying the connections to the power supply. Such small temperature changes may be indicated by a spirit level 16 attached to the furnace chamber I5 and calibrated in degrees. The bubble of the spirit level would be centered for the horizontal position and would move off to one side for a tilt of the furnace. Since the angle of tilt varies the amount of air circulating and hence the cooling of the furnace, the displacement of the bubble would give an indication of the temperature change.

Without further elaboration, the foregoing will so fully explain the gist of my invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to me by the following claims.

I claim:

l. Means for varying the temperature distribution in an elongated furnace having a normal position and closures at each end thereof comprising heating means arranged in said furnace intermediate the ends thereof, vent means at each end of said elongated furnace to provide a multichamber furnace whereby the direction of heat movement through said furnace may be changed by tilting thereof from one position to another, and means for tilting said furnace from said normal position.

2. Heat treating apparatus comprising an'.

elongated chamber having a normal position, closures at each end of said chamber, heating means associated with said chamber intermediate the ends thereof for maintaining a temperature distribution in said chamber, gas inlet and outlet means adjacent each end of said chamber whereby convection currents may pass through said chamber for varying the temperature distribution therein, and'means for displacing said chamber from said normal position in either direction to change the direction of heat movement through said furnace.

3. Heat treating apparatus comprising an elongated chamber having vent means at each end thereof to provide a continuous pathway for the circulation of gases therethrough, heating means centrally arranged in said chamber for producing a temperature distribution varying from a maximum value at the .center of said chamber to a minimum value at the ends thereofi and means for tilting said chamber thereby to vary the circulation of gases therethrough to change said temperature distribution.

4. Heat treating apparatus comprising an elongated chamber having vent means at each end thereof to provide a continuous pathway for the circulation of gases therethrough, said chamber being adapted to be used in a substantially horizontal position, heating means centrally arranged in said chamber for producing a temperature distribution varying from a maximum Value at the center of said chamber to a minimum value at the ends thereof, means for tiling said chamber to effect circulation of gases through said vent means and said chamber, and valve means associated with said vents for controlling the amount of circulating air.

5. Heat treating apparatus comprising an elongated chamber having vent means at each end thereof to provide a continuous pathway for the circulation of gases therethrough, heating means centrally arranged in said chamber, means for tilting said chamber to vary the circulation of gases therethrough, and temperature responsive means for operating said tilting means.

6. Heat treating apparatus comprising a preheating chamber, a heat holding chamber and a cooling chamber arranged in series, heating means associated with .one of said chambers, supporting means for said chambers, pivot means associated with said supporting means whereby s-aid chambers are tiltable from a horizontal position, and means for holding said chambers in any position.

7. Heat treating apparatus comprising a tiltable chamber having a preheating section, a heat holding section and a cooling section -arranged in series, heating means in said heat holding section, supporting means for said chambers, pivot means associated with said supporting means whereby said chamber is tiltable to raise or lower said preheating section land correspondingly lower and raise said cooling portion, and means for holding said chamber in any position.

8. Heat treating apparatus comprising a tiltable chamber having a preheating section, a heat holding section and a cooling section arranged in series whereby material to be treated in said furnace is treated in three stages, heating means in said heat holding section whereby said preheating section and said cooling section derive heat therefrom, means for tilting said chamber whereby the temperatures in said preheating and said cooling sections are varied, and means for holding said chamber in a tilted position.

9. Heat treating apparatus comprising a tiltable chamber having a preheating section, a heat holding section and a cooling section arranged in series for treating material in three stages, heating means in said heat holding section whereby said preheating section and said cooling section derive heat therefrom, said preheating section including an opening and said cooling section including an opening for circulating gases through said chamber, means for tilting saidchamber whereby gases circulate therethrough from said openings for varying the temperatures in said preheating and said cooling sections, and means for holding said chamber in any position.

10. Heat treating apparatus having three stages of operation comprising a tiltable chamber having a preheating section, a heat holding section and a cooling section arranged in series, guide means in said chamber for conveying mate? rial to be treated, heating means in said heat holding chamber whereby said preheating section and said cooling section derive heat therefrom, said preheating section having an opening and said cooling section having an opening for circulating gases through said chamber, means for tilting said chamber whereby gases circulate therethrough from said openings to vary the temperature in said preheating and said cooling sections, and means for holding said chamber in any position.

11. Heat treating apparatus having three stages of operation comprising a chamber having a preheating section, a heat holding section and a cooling section arranged in series, said chamber having a normal position, and means for displacing said chamber frorn said normal position.

12. Heat treating apparatus having three stages of operation comprising a chamber having a preheating section, a heat holding section and a cooling section arranged in series and adapted to be used in the horizontal position, heating means in said heat holding chamber, guide means in said chamber for conveying material to be treated therethrough, and means for varying the temperature in said preheating section and said cooling section comprising air inlet and outlet means associated with each of said preheating and cooling sections and means for tilting said chamber.

13. Heat treating apparatus for successively preheating, heat holding and cooling objects comprising a chamber having a preheating section, a heat holding section and a cooling section arranged in series, heating means in said heat holding section, said preheating chamber and said cooling chamber deriving heat from said heat holding section, and means for tilting said chamber.

14. A heat treating furnace comprising a tiltable body having a plurality of chambers therein, means for supplying heat to said chambers, means for causing said heat to circulate from one to the other chamber, and means for tilting said body to cause said circulating means to change the rate or the direction of movement of the heat through said chambers.

15. Heat treating apparatus comprising an elongated chamber having a normal position, closures at each end of said chamber, heating means associated with said chamber intermediate the ends thereof for maintaining a temperature distribution in said chamber, means for displacing said chamber from said normal position, gas inlet and outlet means adjacent each end of said chamber whereby convection currents of air pass through said chamber for varying the temperature distribution therein, and valve means in said inlet and outlet means.

WALTER C'. HASSELHORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,671,546 Romph May 29, 1928 1,945,652 Martin Feb. 6, 1934 1,972,868 Case Sept. 11, 1934 2,233,474 Dreffein Mar. 4, 1941 FOREIGN PATENTS Number Country Date 3,010 Great Britain Oct. 22, 1908 4,843 Great Britain Sept. 4, 1913 

